Elastic Anomalies in Orbital-Degenerate Frustrated Spinel CoV2O4

Ultrasound velocity measurements were performed on a single crystal of the orbital-degenerate frustrated spinel CoV2O4 in all the symmetrically-independent elastic moduli of the cubic crystal. The measurements of temperature dependence of the elastic moduli observed discontinuous elastic anomalies due to a ferrimagnetic transition at TC = 165 K and another phase transition at T* = 50 K. Additionally, the measurements observed anomalous temperature dependence of the elastic moduli, specifically, non-monotonic temperature dependence in the magnetically-ordered phase below TC, and magnetic-field-sensitive elastic softening with decreasing temperature in the paramagnetic phase above TC. These anomalous temperature variations below and above TC should be driven by the coupling of lattice to magnetic excitations.